This study is designed to determine: 1) the mode(s) of inheritance of mitral valve prolapse and whether it is one or several phenotypically similar conditions; 2) whether, if more than one type of mitral valve prolapse exists on genetic grounds, these can be distinguished by clinical manifestations; 3) the clinical findings which predict which individuals or families are at high risk for complications; 4) the genetic linkage of mitral valve prolapse; and 5) whether an underlying biochemical abnormality can be demonstrated. Initial studies have demonstrated a high degree of reproducibility of echocardiographic findings of mitral valve prolapse and of concordance with auscultatory abnormalities, and have demonstrated additional aspects of phenotypic heterogeneity with regard to dermatoglyphic findings and the occurrence of panic attacks. Studies in the coming year will utilize both nuclear and large extended families to assess modes of inheritance, genetic linkage and patterns of clinical manifestations in order to meet the general objectives of the study. These findings will be related in selected families to biochemical findings in the mitral valve obtained at surgery or autopsy, and to clinical analyses or cardiac arrhythmias and autonomic nervous system dysfunction.